How can you tell if a wall is a suporting wall?

substructure do you always use this method

yes ,knock em down and if the upstairs becomes unsteady or collapses then it was supporting ,or better still get a structural engineer round and he will tell you ,

You need to get a builder round to have a look, depends which way the floors run etc, and if there are any walls above.

easiest way is to lift a carpet upstairs to see if the floor joists run into the wall in question. if you cant lift a carpet to see, then knock on wall to see if it sounds solid or hollow. if hollow sounding its a stud wall and non supporting. if hard sounding it will mos tlikely be a load bearing wall. always best to get pro advice though before getting the hammers and chisels out yourself.